| Summary: | 碩士 === 國立臺灣海洋大學 === 機械與機電工程學系 === 103 === In this study, numerical simulations of a bluff-body structure with multiple holes were performed using ANSYS Fluent, a software application for computational fluid dynamics (CFD) analysis. Using a fixed gas flow and a non-reactive gas, the effects of number of holes, type of gas, and jet inclination angles were calculated. The bluff body with multiple holes can transform axial momentum into radial and tangential momentum, increase the swirl number (S) and generate strong turbulence intensity (T.I.). The concentration distribution behind the mixing of central carbon-dioxide jet and annular air jet was utilized to analyze the mixing efficiency.
Three bluff bodies with differing numbers of holes (3, 6, and 12 holes), three different jet inclination angles (45°, 60°, and 90°), and one control set of streams without a bluff body (i.e., pure jet) were designed for the analysis. Each test was conducted using the same inlet central/annular flow rate. Analysis of the numerical simulation results revealed that the bluff-body effectively increased the length of the recirculation zone by increasing the contact area between the central and annular flows. The bluff-bodies with multiple holes also significantly increased the swirl number and the turbulence intensity with comparing those behind the pure jet. The maximum turbulence intensity occurred behind the bluff body with six holes and a jet inclination angle of 45°. This T.I. is 7.5-fold stronger than that for the pure jet. In addition, the concentration of carbon dioxide decreased to less than 33% as the turbulence intensity increased. A bluff-body with three holes and a jet inclination angle of 45° achieved the lowest concentration of carbon dioxide.
Index Terms: swirl-jet flow, bluff body with multiple holes, computational fluid dynamics (CFD), mixing efficiency
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